1. Field of the Invention
This invention relates to an optical laminate and to a method of manufacturing the same.
2. Related Background Art
In image display devices such as cathode ray tube displays (CRT), liquid crystal displays (LCD), plasma displays (PDP) and electroluminescence displays (ELD), the outermost surfaces are provided with optical laminates exhibiting various functions such as anti-reflection, hardness and transparency.
In the past, a wide variety of structures have been proposed for optical laminates, and examples include those with a substrate, antistatic layer, hard coat layer and low refractive index layer laminated in that order, and those with a substrate, hard coat layer, high refractive index layer and low refractive index layer laminated in that order.
Usually when a functional layer such as an antistatic layer or high refractive index layer is formed on a substrate or a hard coat layer, its coating or fixing of the film in the production line is hampered unless the functional material comprising the antistatic agent or fine particles is dispersed in a binder material. A “binder” in this case represents a resin component such as a monomer, oligomer or prepolymer that undergoes crosslinking by heat or ionizing radiation (UV, EB or the like).
When a functional layer is formed to modulate the conductivity or refractive index, it has been, therefore, common to use a coating composition containing a function-exhibiting material dispersed in a binder material, with the concentration adjusted using a solvent or the like (for example, see Patent Documents 1 and 2).
However, compositions dispersed using a binder material have been associated with various problems including a short pot life, the need for multiple dispersing steps, reduced dispersion stability, gelling, and deterioration of the optical characteristics of the coated film with time. Care must, therefore, be taken in selecting the binder material, and a considerable amount of time has been spent investigating new materials.
Patent Document 3 discloses a solvent that swells or penetrates the substrate as an essential factor which allows triacetylcellulose (TAC) or the like to prevent interference patterns. Furthermore, since the refractive index near the interface between the substrate and the hard coat layer must vary in a continuous manner, it is presumed that the hard coat material penetrates into the substrate by the solvent.
However, such penetration makes it impossible to maximize the function of the functional material. Moreover, because a hard coat (binder) is indispensable, even though a functional material is present in the binder it is not possible to realize contact of the functional materials without a binder as according to this invention; therefore, high function cannot be exhibited.
Patent Document 4 also discloses a solvent that swells or permeate the substrate as an essential factor which allows TAC or the like to prevent interference patterns. There is also disclosed that coating of the hard coat material with such a solvent forms a resin layer as the solvent dissolves the substrate, thus allowing discontinuous microirregularities to be formed at the interface, but this method also requires a binder as in Patent Document 3, and therefore, does not allow the high function of the functional material to be exhibited.
The invention described in Patent Document 5 employs a step using a solvent that dissolves the substrate, but the resin coated together with the solvent is required to penetrate the substrate. Therefore, since this proposed method also differs from this invention while requiring a translucent resin, it cannot yield products that maximize the function of the functional material.    [Patent Document 1] Japanese Patent Laid-open (Kokai) Publication No. 2000-94590    [Patent Document 2] Japanese Patent Laid-open (Kokai) Publication No. 2003-75603    [Patent Document 3] Japanese Patent Laid-open (Kokai) Publication No. 2003-131007    [Patent Document 4] Japanese Patent Laid-open (Kokai) Publication No. 2003-205563    [Patent Document 5] Japanese Patent Laid-open (Kokai) Publication No. 2003-121618